1. Field of the Invention
The present invention is generally related to a marine propulsion device and, more particularly, to an outboard motor with a catalyzed exhaust system.
2. Description of the Related Art
Those skilled in the art of marine propulsion devices are familiar with many different types of structures and systems provided to direct the flow of exhaust gas from the engine of the marine propulsion device, such as an outboard motor. In addition, those familiar with marine engines are aware of many different types of engine cooling systems which direct a coolant, such as water, to flow in thermal communication with portions of the engine and its components that receive heat from the internal combustion process. Those familiar with marine propulsion devices are also aware of many different arrangements for catalyzing the exhaust from marine engines.
U.S. Pat. No. 4,772,236, which issued to Takahashi on Sep. 20, 1988, describes an exhaust gas purifying device for a marine engine. An outboard motor with an improved catalyst system for treating the exhaust gases regardless of whether they are delivered to the atmosphere through an above the water exhaust gas discharge or a below the water exhaust gas discharge is described.
U.S. Pat. No. 5,378,180, which issued to Nakayama et al. on Jan. 3, 1995, describes an exhaust system for an outboard motor. A catalyst is positioned in the exhaust system downstream of the point where the exhaust pipe terminates in the expansion chamber so as to preclude interference with the exhaust timing. The catalyst bed is removable for ease of servicing without necessitating removal of the outboard motor from the attachment to the associated water path and a trap device is provided for precluding water from entering the engine through its exhaust port.
U.S. Pat. No. 5,556,311, which issued to Fujimoto on Sep. 17, 1996, describes an outboard motor exhaust cooling system. A catalytic exhaust system for an outboard motor is described wherein the catalyst is positioned in the driveshaft housing to remove the force of heat from the powerhead. However, the catalyst is contained within a field compartment in the driveshaft housing lower unit. In order to protect the catalyst from water, a trap section is positioned in the powerhead and this is water cooled by a source of water which has not passed through the engine for its cooling prior to delivery to the trap section.
U.S. Pat. No. 5,911,610, which issued to Fujimoto on Jun. 15, 1999, describes an outboard motor exhaust system. A catalytic exhaust system for an is outboard motor having an engine positioned in a cowling is described. The exhaust system leads from an exhaust port of the engine to a discharge from the motor. A catalyst is positioned in the exhaust system for catalyzing exhaust gases. A first port is positioned in the exhaust system downstream of the catalyst through which an exhaust gas probe may be selectively extended for obtaining an exhaust gas sample.
U.S. Pat. No. 6,632,110, which issued to Kato on Oct. 14, 2003, describes an exhaust catalyst for an outboard motor engine. The catalyst assembly for an outboard motor includes a branched passage connecting the main exhaust passages with a catalyst device. The outboard motor can include various exhaust passages and features for controlling and discharging the flow to and from the catalyst device.
U.S. Pat. No. 6,662,555, which issued to Ishii on Dec. 16, 2003, describes a catalyzer arrangement for an engine. It includes an improved construction that does not require a large space for furnishing a relatively large volume catalyzer. The engine is surrounded by a protective cowling. A cylinder body of the engine has a plurality of cylinder bores spaced apart from each other. The engine also has an exhaust manifold to gather exhaust gases from the respective cylinder bores. An exhaust passage is coupled to the manifold and extends, at least in part, within a space defined between a side surface of the cylinder body and the protective cowling. At least one catalyzer is disposed in the exhaust passage.
U.S. Pat. No. 7,216,638, which issued to Burk et al. on May 15, 2007, discloses a control of exhaust gas stoichiometry with inducted secondary air flow. A method for operating a marine engine uses four valves to control the flow of secondary air that is inducted into each of the cylinders of an engine. An oxygen sensor is disposed in an exhaust passage downstream from the cylinders and upstream from a catalytic converter. A carburetor is calibrated to provide a richer than stoichiometric air/fuel ratio so that inducted secondary air through the valve associated with each cylinder can result in a stoichiometric ratio of air flowing into each cylinder. The cylinders are each provided with their own valve in order to allow the air/fuel ratios to be equalized for each cylinder regardless of the configuration and geometry of the intake manifold and its associated circuits.
U.S. patent application Ser. No. 11/966,699, which was filed on Dec. 28, 2007 by Ito et al., describes an exhaust system for an outboard motor. An outboard motor includes a multi-cylinder engine which includes cylinders longitudinally oriented and vertically parallel in a cylinder block, a cylinder head arranged at a rearward position of the cylinder block, and a crank case arranged at a forward position of the cylinder block, the cylinder head having an outlet of an exhaust port at one side thereof. An exhaust system for the outboard motor includes an exhaust manifold which communicates the outlet of the exhaust port with an exhaust outlet opening, the exhaust manifold including a first exhaust gas passage extending in a vertical direction for gathering exhaust gas discharged from the outlet of each exhaust port and a second exhaust gas passage extending in a vertical direction adjacently to the first exhaust gas passage, and a catalyst unit is provided on the way of the second exhaust gas passage.
The patents described above are hereby expressly incorporated by reference in the description of the present invention.